The present invention relates to a hitch device for a working vehicle.
Publication WO 2004/056168 makes known a hitch device for a working vehicle designed as a tractor, the coupling structure of which is supported at the top on a frame structure of the tractor via an upper lifting shaft. The lifting shaft is coupled with two reciprocating cylinders that are hingedly located on the frame structure of the tractor via lifting arm systems having a single-piece or multiple-piece design. On the front side, the lifting arm system includes two—or pairs of—coupling elements that are positioned in the vertical direction and whose lengths may be adjusted—and which are hydraulically adjustable reciprocating cylinders in this case—that are hingedly connected at their free ends with lower linkages located in pairs on the underside.
The lower linkages are acted upon in a hinged manner on the frame structure of the tractor in a region that is located below the vehicle axis. By applying or releasing pressure to the reciprocating cylinders connected with the lifting shaft, the coupling frame and the hitch device connected thereto may be raised or lowered in the vertical direction. A special position of the coupling frame and the hitch devices attached thereto may also be adjusted by applying pressure to or releasing pressure from the reciprocating cylinders, which are located in a nearly vertical position. Given that the vertically-extending reciprocating cylinders act on the lower linkages in a central region, bending occurs in the lower linkages, the lifting shaft rotates, and pressure is applied to the arresting devices assigned to the free ends of the lower linkages, in particular when a load is introduced asymmetrically.
A design of a hitch device that does not include a lifting shaft was made known in EP 1 360 886 in order to optimize the loads that act on the hitch device, and with consideration for the fact that the application of a hitch device of this type must be highly flexible. Depending on the degrees of freedom desired, a hitch device of this type that is composed of six coupling elements includes up to six adjustable-length coupling elements, or two adjustable-length coupling elements and a large number of rigid coupling elements, via which a hitch device is supported and guided on a working vehicle, e.g., a tractor. Given that the coupling elements are located directly on the tractor or a coupling frame, or directly on the working device, only tensile and compression loads occur in the coupling elements.
The coupling elements of the hitch device located on the right and left sides are interconnected in a hydraulic manner, however, so that, when loads are introduced into the hitch device in an asymmetrical manner, as takes place, e.g., when working with a plow or when mowing using lateral mowing units, loads are applied to the coupling elements asymmetrically. To prevent damage from occurring to the coupling elements, which are typically designed as reciprocating cylinders, they must therefore be considerably oversized in design. In addition, given that the hitch device is coupled with the tractor exclusively via the coupling elements, the coupling elements must be controlled in a complicated manner so that the particular hitch device performs the desired reciprocating motion in a precise manner.